Controlling device



Nov. 19, 1940. J. M. BARTHOLOMEW' CONTROLLING DEVICE Original Filed Dec. 2, 1955 M Z n2 5. m w

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Patented Nov. 19, 1940 UNITED" STATES PATENT OFFICE CONTROLLING DEVICE Jess M. Bartholomew, Michigan. City, Ind., as-.

signor to Sullivan Machinery Company, a corporation of Massachusetts Original application December 2, 1935, Serial No. 52,552. Divided and this application November 9, 1936, Serial Nor109,865. Renewed October 1s This invention relates to controlling devices, .and more particularly to controlling devices especially adapted to, but 'not exclusively limited to, pump control.

uniform and high demand prevails (near the maximum pumping capacity), itis desirable to operate pumping apparatus, as for example, compressors, upon a system where there is no stopping of the pump drive, but instead an interrupably longer period of demand, it is desirable, to,

reduce'wear and to economize on operating medium, to interrupt the drive of the pumping apparatus completely and to bringthe same to a stop until such time as theconsumption of the pumping to preclude the reduction of the availablepumped fluid to less than a desired minimum. When operating upon the first system, it is considered good practice to effect interruption and reduction of pumping upon comparatively small changesjn the available quantity of fluid; For example, when a compressor is set to unload at 100 pounds, it will be reloaded upon a comparatively small pressure drop, say to 95 pounds.'

Under other circumstances where, for example, during a night shift there might be compara- .tively little demand for pumped fluid. and a compressor adequate to supply the daytime needs would, if operated on the load and unload sys tem, operate for long periods unloaded and use considerable quantities of operating medium without benefit resulting, the stop and start sys- .tem may be employed; and, while it will not be desired to alter the maximum value of air pres- ;sure and to unload, upon the attainment of a pressure of pounds per square inch, it is possible, without undue loss of efiiciency and with sound economy for the entire system, to allow Under certain conditions, where a 'relatively pumped fluidagain makes necessary further vide a controlling device governedby the pump discharge pressure which shall be eifective to cause interruption in the delivery of pumped fluid under other systems of operation, upon the attainment of approximately the same maximum discharge pressure, and by such, to vary and'adjust the minimum pressure of the system between wide rates. It is obvious that such devices are not limited in their, utility to controlling pump discharge, but may be advantageously used in systems for controlling pressure generated or produced in various other ways.

It is an object of my invention to provide an improved device which embodies improvements in the change-over from one system to another of pressure control, and operative automatically to effect a change in one of the pressure limits upon such change-over. It is another object of my invention to provide an improved device of the character set forth in which the automatic change may be efiected to affect the minimum pressure limit. It is a still further object of my invention to provide an improved device in which the change in minimum pressure limit shall not' appreciably affect the maximum pressure limit. A further object of my invention is to provide an improved adjustable pressure-responsive pilot mechanism. Still another object is to provide an improved snap action for a pilot mechanism having associated therewith means for varying the lower snap point while leaving the higher snap point unchanged, and providing for said improved pilot mechanism means whereby the snap point may be varied when the basic system of control of the apparatus which said pilot mechanism controls is changed. Still another object of the invention is to provide air-improved pilot means having provision for various maximum and minimum variations, and having controlling mechanism associated therewith operative to alter the minimum value without varying the maximum value, when said system, of which said pilot mechanism forms a part, is shifted from one of its operating systems to another. Other objects I and advantages of the invention will hereinafter more fully appear.

. In the accompanying drawing, in which one illustrative embodiment which the invention may- Fig. 2 is a vertical section on the plane of the line 2-2 of Fig. 1.

Fig. 3 is a fragmentary detail view showing a modification.

Fig. 4 is a wiring diagram of a system illustrating one application of my improved pilot valve 5- mechanism.

As my improved pilot valve mechanism may best be understood by reference to one illustrative application thereof, I have shown in Fig. 4 a simple system in accordance with which the invention maybe utilized. Referring to Fig. 4, it will be observed that a suitable driving motor I arranged to receive current from a power line 2 upon closure of a main line switch 3 is connected in driving relation with a compressor 4, herein of the multi-cylinder type. The compressor delivers through connections l2, I2 to a common discharge connection l3, which leads to a receiver l4, the pressure from within which is conducted through a pipe I5 to an electrically controlled valve mechanism I 6 operative upon energization of its controlling winding to cause compressor loading, and upon deenergization of the winding to cause compressor unloading. As the present invention relates only to the structure of my improved pilot mechanism, one of whose functions is to control, in this illustrative system, the supply of operating medium to the winding 30, details of the construction of the valve mechanism l6 and of the unloading mechanism controlled thereby need no further disclosure. The function of this application may again be summarized by stating that by energization of the winding 30 the compressor 4 is loaded, and upon deenergization of the winding 30 the compressor is unloaded. Now, it will be observed from the description which has been given that the compressor 4 will not pump any fluid unless its driving motor I is supplied with current, and that it will not deliver any pumped fluid if the magnet 30 is deenergized, even though the motor I may be driven. It will be evident moreover, that if its winding .30 is deenergized whenever the motor I is first supplied with current, the compressor may be started unloaded, and with a less current consumption. I

The switch 3 is of the normally open type and is adapted to be closed by a solenoid 32. The solenoid 32 is connected at one end by a conductor 33 with the secondary 34 of a transformer 5035 whose primary 36 is connected across two of the power lines 2. The other end of the solenoid 32 is connected to a conductor 31.

The magnet winding 30 is connected at one end to a conductor 38 and at its other end to a 55 conductor 39. The conductor 39 leads from a time delay relay of well known commercial construction, marked TDR in the drawing, and the conductor 39 is adapted to be connected, upon the circuit-closing operation of the time delay gorelay, with a conductor 40 leading to the end of the transformer secondary 34 to which the conductor 33 is also connected. The time delay relay is also connected by a conductor 4| to the conductor 31, and when a circuit is established be- 55 tween the conductor and the end of the transformer secondary 34 to which the conductor 40 is not connected, the time delay relay is set in operation, and after a predetermined time interval closes a circuit between the conductors 40 and 39. 7 As this function and the structure of these devices are well known, and this time delay relay mechanism may assume many forms and is a stardard article of manufacture which can be bought in the open market, further description of its mode 75 of operation is unnecessary. Beyond its point of connection with the conductor 4|, the conductor 31 is connected to other conductors 42 and 43 respectively. These lead respectively to contacts 44 and 45 in a so-called transfer switch 46, and this transfer switch also is provided with other contacts 41 and 48 and with a-inovable contact 49, which may be caused, in one position of the switch, to connect the contacts 44 and 41, and in an opposite position to connect the contacts 45 and 48. The contact 48 is connected by a conductor 50 and a further conductor 5| to the end of the transformer secondary 34 to which conductors 33 and 40 are not connected. The contact 41 has a conductor 52 connected thereto, to which. the conductor 38 leads, and also is connected, by a conductor 53, to one of the contacts of a Mercoid switch M whose other ,contact is connected by a conductor 54 to the conductor 5|. The "Mercoid switch forms a portion of a pilot mechanism, generally designated P, which constitutes the illustrative embodiment of my invention, which I am claiming in this divisional application. The pilot mechanism P, as shown in Fig. 1, comprises a diaphragm 55 which is subjected, upon its exterior, to receiver pressure through a connection 56, which opens into a chamber 51 surrounding the diaphragm 55. It will be noted that the diaphragm 55 is operatively connected to and tends to efiect a swinging movement of an arm 58 about a pivot 59 provided by a casing 60 housing the component elements of the pilot mechanism P. The range of movement ,of the arm 58 is limited by stops 6| and 62. -The arm 58 forms .a portionof a trigger or snap mechanism, generally designated 63, and is subjected to the endwise pressure of a spring 64 whose compression may be varied by varying the projection within the casing 60 of a pin 65, which provides a reaction point for the end of the spring 64 remote from the arm 58.. A link 65 connects the free end of the arm 58 with the switch M, which is herein shown as of the so-called Mercoid type and contains mercury, as at 61, which in the tilted position of the switch shown in Fig. 1 establishes an electric circuit between the conductors 53 and 54. The pin 65 is disposed substantially in alinement with the pivot 59, and accordingly the spring 64 exercises little effect upon the movement of the arm 58 when said arm is in depressed position, i. e. as shown in Fig. 1. A primary control spring 58 acting in opposition to the diaphragm 55, provides substantially exclusive control of the movement of the arm 58 upwardly, and provides a major load thereon; and the adjustment of the compression of the spring 68 varies the maximum pressure limit of operation of the apparatus P. When the arm 58 is inits upwardly tilted position, which it assumes upon the attainment of the maximum desired receiver pressure (in which position the switch M is swung about the pivot m and the mercury 61 flows away from the conductors 53 and 54 and opens the circuit between said conductors) the spring 64 ,exerclses a very substantial force and plays a very material part in determining the pressure at which movement of the arm 58 in the downward direction shall take place. It will be found that .the pressure range between the opening and closing of the switch M-can be markedly varied simply by varying the compression of the spring 64,

without materially varying the pressure at which opening of the switch will occur; and the pin 65,

upon being variously projected longitudinally,-

will provide for the necessary variation in the compression of the spring 541 to secure a large or the pressure at which the spring 68 will be cffective to cause re-closing of the switch M.

Many ways of varying the projection of the pin 65 may be employed. In Figs. 1, 2 and 4, one simple and somewhat diagrammatic mode of accomplishing this function is illustrated. It

' will be noted that the transfer switch 46 is provided with a sprocket 16 turning therewith and connected by a chain 1| with a sprocket 12 mounted upon a shaft 13 whose axis is at right angles to the axis of the pin 65. The shaft 13 carries a cam 14 which, in the ofi position (the intermediate position) of the transfer switch 46, simply holds the pin 65 in the position shown in Fig. 1. Upon movement of the transfer switch 46 to connect the contacts 44 and 41, the cam 14 will project the pin 65 substantially to the right in-Fig. 1, and then hold it there. Upon movement of the transfer switch from the position shown in Fig. 4 to a position connecting the .contacts 45 and 48, no movement of the cam 14 affecting the position of the pin 65 will take place. It will be noted that the cam 14 has a long, low arcuate'portion 16 and a'quadrantal high operating portion 11.

If it'be desired to vary the pressure difference produced by moving the cam 14 into pin-protruding position, this may be easily accomplished by providing a cam of varying radial dimension and sliding the cam longitudinally along its shaft, of course providing suitable holding means to maintain it in desired position; Such an arrangement is shown in Fig. 3, in which the cam portion 11' is sloping and the cam is movable by the adjusting mechanism 18, held in different positions by the pin devices 19, -to provide different movements, as maybe desired, of the pin 65.

This mechanism is merely illustrative of a wide variety of devices which may be employed.

The mode of operation of the apparatus so far described will be readily understood from what has been said. In Fig. 4 the apparatus is shown with the parts in the relative positions they would occupy before the motor is started. The switch 46 is in neutral position and must be moved in one directionor the other to place the system in operation. It will be borne in mind that in the position of the parts shown, the solenoid 30 is de-energized and accordingly the compressor is unloaded. Depending upon which direction the switch mechanism 46 is turned, the system will operate either with,con-

tinuous running of thecompressor and periodic loading and unloading, or with intermittent running of the compressor and'startingeach time unloaded. Continuous running of the compres-- sor will tabe place when switch 46 is moved iecited into the casing 66, as would occur when the cam portion 11 contacts the end of the pin, the switch will open still at approximately 100 pounds, but will not close again until the pressure falls 01f perhaps-to 80 pounds.

Now let us consider that the operator wishes to start up the system and to cause the same .to operate on the continuous running, loadingand-unloading system. He will therefore turn the switch 46 through 90 counter-clockwise in Fig. 4 and cause the contact 43 thereon to connect the contacts 45 and 46. Immediately, current will flow from the transformer secondary 34 through the circuit including the conductor 5|, conductor 50, contact 43, contact -49, contact 45, conductor 43, conductor 31, solenoid 32 and conductor 33; and the switch 3 will close and the motor will start. Simultaneously with the establishment of the circuit through the switch operating solenoid 32, a circuit will be established including the transformer secondary 34, conductor 5|, conductor 50, contacts 48, 49 and 45, conductor 43, conductor 31, the time delay relay operating circuit, and conductor 46; and the time delay relay will close its internal contactor after a predetermined time interval.

When the time delay for which the time delay relay is set, has elapsed, current will likewise flow through a circuit including the transformer secondary 34, the conductor 6|, conductor 54, switch M if the latter be closed, conductor 53, conductor 38, solenoid 30, conductor 39, time delay relay TDR, and conductor 40w It will therefore be evident that only when the switch M is closed will the compressor load; and it will further be evident that the compressor will load and unload under the control of the movements of the switch gvl as long as the system is setto operate in the manner mentioned, that is, as long as the switch 46 remains in the position last described. During this operation, loading 35 and unloading will be brought about as a result of the pressure changes, loading occurring when the pressure drops to,"say, 95 pounds, and .unloading occurring when the pressure rises to 100 pounds. f 40 When it is desired to operate on the stopand-start system, the operator, instead of positioning the switch 46 with 'the contact 49 in lower position,. will'move the switch 46 to cause the contact 49 to connect the contacts 41- and 44. Then the following operations will occur. Only when the switch M is closed will anything take place. When the switch M is closed, however, a circuit will be established including transformer secondary 34, conductor 5| conductor 54, mercury 50 61, conductor 53, conductor 52, contacts 41, 49 and 44,. conductor 42, conductor 31, solenoid 32, and conductor 33; and the motorswitch 3 will then be closed. This will start thernotor. Concurrently with the establishment of' tl'ie circuit lust described, there will also be established a circuit including transformer secondary 34, conductor 5|, conductor 54, mercury 61,"conductor 53, conductor 52, contacts 41, 49 and 44, conductor 42, conductor 31, conductor 4 the operating device of the time delay relay, and conductor 46. Accordingly, the time delay relay will beset in operation concurrently with the closing of the motor circuit. Then after the "time lapse com-'- pelled by the time delay relay, a further circuit will be established including the transformer secondary 34, conductor 5|, conductor 54, mercury 61, conductor 53, conductor .36, winding 36, conductor 39, the time delay relay,'and conductor 46; and the compressor will be loaded 7 due to the operation of the pilot mechanism l6 to shut off further fluid supply to the unloading plungers and to vent the latter to atmosphere. Now it is important to note that as the switch 46 was moved to position the cont-act 49 in engagement with contacts 41 and, the sprocket 10, chain II, and sprocket 12 moved the cam 14 and brought its high point TI into engagement with the plunger 65, and forced that plunger inwardly, thereby increasing the compression of the spring 64 and making necessary a much greater receiver pressure drop before the switch M will move from open to closed position. Accordingly, when rising receiver pressure has once caused opening of the switch M and stopping of the compressor through the breaking of the crcuit through the solenoid 32, a much more marked pressure drop will be necessary before the switch M will reclosesay, a drop from 100 to 80 pounds. However, due to the spacial relation of the parts, this result, which follows upon the protrusion of the pin 65 into the casing 60, will not materially aifect the upper pressure limit of 100 pounds.

From the foregoing description, it will be observed that I have provided a pilot apparatus adapted effectually to control the operation of a pumping system either when the latter is connected up for load-and-unload operation or for starting and stopping operation, the same pilot mechanism being employed in each case and varying in responsiveness to dropping pressures while retaining its upper operating value substantially unchanged.

While there is in this application specifically described one form and a modification which the inventFon may assume in practice, it will be understood that this form and modification of the same are shown for purposes of illustration and that the invention may be further modified and embodied in various other forms without departing from its spirit or the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent is:

1. In a pressure-responsive mechanism, a control element, and pressure-responsive means for moving the same in one direction on attainment of a predetermined maximum pressure and for moving the same in an. opposite direction on' attainment of a predetermined minimum pressure including a member responsive to the pressure to be controlled, a lever operatively connected with said member and with said control element, yielding means directly opposing movement of said lever by said member, and yielding means for exerting a pressure longitudinally of said lever in alinement with whose direction of reaction said lever is disposed in one limiting position thereof.

2. In a pressure-responsi e mechanism, a control element, and pressure-responsive means for moving the same in one direction on attainment of a predetermined maximum pressure and for moving the same in an opposite direction on attainment of difierent predetermined minimum pressures including a member responsive to the pressure to be controlled, a lever operatively connected with said member and with said control element, yielding means directly opposing movement of said lever by said member, yielding means for exerting a pressure longitudinally of said lever in alinement with whose direction of reaction said lever is disposed in one limiting position thereof, and means for varying the pressure exerted by said last mentioned yielding means.

3. In a pressure-responsive mechanism, a control element, and pressure-responsive means for moving the same in one direction on attainment of a predetermined maximum pressure and for moving the same in an opposite direction on attainment of a predetermined minimum pressure including a member responsive to the pressure to be controlled, a lever operatively connected with said member and with said control element, yielding means directly opposing movement of said lever by said member, and yielding means for exerting a pressure longitudinally of said lever into alinement with whose direction of reaction said lever is movable upon attainment of the predetermined minimum pressure and out of alinement with which said lever is movable again only on attainment of said predetermined maximum pressure.

4. In a pressure-responsive mechanism,- a control element, and pressure-responsive means for moving the same in one direction on attainment of a predetermined maximum pressure and for moving the same in an opposite direction on attainment of different predetermined minimum pressures including a member responsive to the pressure to be controlled, a lever operatively'connected with said member and with said control element, yielding means directly opposing movement of said lever by said member, yielding means for exerting a pressure longitudinally of said lever into alinement with whose direction of reaction said lever is movable on attainment of the predetermined minimum pressure and out of alinement with which said lever is movable again only on attainment of said predetermined maximum pressure, and means for varying the value of said minimum pressure whose attainment is effective to cause the movement of said lever into alinement with the direction of reaction of said second mentioned yielding means.

5. In a pressure-responsive mechanism, control means, and pressure-responsive means for moving said control means into one position on attainment of a predetermined maximum pressure and into another position on attainment of a predetermined minimum pressure including a member responsive to the pressure to be controllcd, an element operatively connected with said member and said control means, yielding means directly opposing movement of said element by said member, and yielding means for exerting a pressure longitudinally of said element in alinment with whose direction of reaction said element is disposed in one limiting position thereof.

6. In a pressure-responsive mechanism, control means, and pressure-responsive means for moving said control means into one position on attainment of a predetermined maximum pressure and into another position on attainment of different selected predetermined minimum pressuresv including a member responsive to the pressure to be controlled, an element operatively connected with said member and said control means, yielding means directly opposing movement of said element by said member, yielding means for exerting a pressure longitudinally of said element in alinement with whose direction of reaction said element is disposed in one limiting position thereof, and means for varying the pressure exerted by said last mentioned yielding means.

7. In a pressure-responsive mechanism, control means, and pressure-responsive means for moving said control means into one position on attainment of a predetermined maximum pressure and into another position on attainment of a predetermined minimum pressure including a member responsive to the pressure to be controlled, an element operatively connected with said member and with said control means, yielding means directly opposing movement of said element by said member, and yielding means for exerting a pressure longitudinally of said element in alinement with whose direction of reaction said element is disposed upon attainment of the predetermined minimum pressure.

8. In a pressure-responsive mechanism, control means, and pressure-responsive 'means for moving said control meansinto one position on attainment of a predetermined maximum pressure and into another position on attainment of difierent selected predetermined minimum pressures including a member responsive to the pressure to be controlled, an element operatively connected with said member and with said control means, yielding means directly opposing movement of said element by said member, yielding means for exerting a pressure longitudinally of said element in alinement with whose direction of reaction said element is disposed upon attainment of the. predetermined minimum pressure, and means for varying the value of said minimum pressure whose attainment is effective to cause the movement of said element into alinement with the direction of reaction of said second mentioned yielding means.

9. In a pressure-responsive mechanism, control means, a yieldable snap-action actuat means for said control means including yielding means and .an element on which one end of said yielding means exerts a thrust, means limiting movement of said element in one direction to attainment to a position in alinment with said yielding means, means responsive to the pressure to be controlled for actuating said snapable element acting on the other end of said yielding means.

10. In a pressure-responsive mechanism, a control element, and pressure-responsive means for moving the same in one direction on attainment of a predetermined maximum pressure and for moving the same in an opposite direction on attainment of different selected predetermined minimum pressures including a member responsive to the pressure to be controlled, a lever operatively connected with said member and with said control element, yielding means directly opposing movement of said lever by said member, yielding means for exerting a pressure longitudinally of said lever in alingnent with whose direction of reaction said lever is disposed" in one limiting position thereof, and means for varying the pressure exerted by said last mentioned yielding means including a cam of varying radial dimen-" sions and means movable by said cam generally longitudinally of said last mentioned yielding means for varying thepressure exerted by said last mentioned yielding means.

'11. In a pressure-responsive mechanism, a control element, and pressure-responsive means for moving the same in one direction on attainment of a predetermined maximum pressure and for moving the same in an'opposite direction on attainment of difierent selected predetermined minimum pressures including a member responsive to the pressure -to becontrolled, a lever operatively connected with said member and with said control element, yielding means directly opposing movement of said lever by said member, yleldingmeans for exerting a pressure longitudinally of said lever in alinement with whose direction of reaction said lever is disposed on attainment of the predetermined minimum, pressure, and means including a cam of varying radial dimensions and means movable by said cam generally longitudinally of and supporting said yielding means for varying the value of the minimum pressure whose attainment is effective to cause movement of said lever into alinement with: the direction of reaction of said second mentioned yielding means.

12. In a pressure-responsive mechanism. control means, and pressure responsive means for moving said control meansinto one position on attainment of a predetermined maximum pressure and into another position'on attainment of different selected predetermined minimum pres-. sures including a member responsive to the pres- -sure to be controlled, an element operatively connected with said member and said control means, yielding means directly opposing movement of said element by said member, yielding means for exerting a pressure longitudinally of said element in alinement with whose direction of reaction said element is disposed in one limitifig position thereof, and means for varying the pressure exerted by said last mentioned yielding means including a cam of varying radial dimensions and means movable by said cam longitudinally of and supporting said last mentioned 30 yielding means.

13. In a pressure-responsive mechanism, control means, and pressure-responsive means for moving said control means into one position on attainment of a predetermined maximum pres-- sure and into another position on attainment of diflerent selected predetermined minimum pressures including a member responsive to the pressure to be controlled, an element operatively connected with said member and with said control means, yielding means directly opposing movement of said element by said member, yielding means for exerting a pressure longitudinally oi! said element into alinement with whose direction of reaction said element is movable only upon attainment of the predetermined minimum pres-' sure and out of alinement with which said element is movable again only upon attainment of said predetermined maximum pressure, and means for varying the value of said minimum pressure whose attainment is effective to cause the movement of said element into alinement with the direction of reaction of said second mentioned yielding means, said means including a cam of varying radial dimensions and means movable by said cam longitudinally of and supporting said yielding means.

14. In a pressure-responsive mechanism, a control element. and pressure-responsive means for moving the same'in one direction on attainment of a predetermined maximum pressure and for moving the same in an opposite direction on attainment of different predetermined minimum pressures including a member responsive to the pressure to be controlled, a lever operatively connected with said member and with said control element, yielding means directly opposing movement of said lever by said member, yielding means for exerting a pressure longitudinally of said lever into alinement with whose direction of reaction said lever is movable on attainment of the predetermined minimum pressure and out of alinement with which said lever is movable again only on attainment of said predetermined maximumpressure, and means for varying the pres- 1 sure exerted by said last mentioned yielding means thereby to vary the value of said minimum pressure whose attainment is effective to cause the movement of said lever into alinement 'withthe direction of reaction of said second mentioned yielding means.

nected with said member. and with said control means, yielding means directly opposing movement of said element by said member, yielding means for exerting a. pressure longitudinally of said element in alinement with whose direction of reaction said element is disposed upon attainment of the predetermined minimum pressure, and means for varying the pressure exerted by said last mentioned yielding means thereby to vary the value of said minimum pressure whose attainment is effective to cause the movement of said element into alinement with the direction of reaction of saidsecond mentioned yieldin means.

16. In a pressure responsive mechanism, control means, and pressure-responsive means for moving said control means into one position on attainment of a predetermined maximum pressure and into another position on attainment of different selected predetermined minimum pressures including a member responsive to the pressure to be controlled, an element operatively connected with said member and with said control means, yielding means directly opposing movement of said element by said member, yielding means for exerting a pressure longitudinally of said element into alinement with whose direction of reaction said element is movable only upon attainment of the predetermined minimum pressure and out of alinement with which said element is movable again only upon attainment of said predetermined maximum pressure, and means for varying the pressure exerted by said last mentioned yielding means thereby to vary the value of said minimum pressure whose attainment is efiective to cause the movement of said element into alinement with the direction of reaction of said second mentioned yielding means, said means including a cam of varying radial dimensions and means movable by said cam longitudinally of and supporting said last mentioned yielding means.

17. In a pressure-responsive mechanism, a control device, and pressure-responsive means for moving the same in one direction on attainment of a predetermined maximum pressure and for moving the same in an opposite direction on attainment of different selected predetermined minimum pressuresincluding a member responsive to the pressure to be controlled, an element operatively connected with said member and with said control device and movable to shift the eflective position of said control device, means for exerting a force on said element suificient to maintain the same stationary until said maximum predetermined pressure is attained and operative to return said element to its stationary position mentioned upon a suflicient reduction in the pressure to be controlled, and means adjustable while the predetermined maximum pressure at which said device will be moved in one direction is maintained at least substantially the same, to alter the drop in pressure which must occur in order that said force-exerting means may return said element to its stationary position mentioned.

18. In a pressure responsive mechanism, a control element, and pressure-responsive means for moving the same in one direction on attainment of a predetermined maximum pressure and for moving the same in an opposite directin on attainment of different selected predetermined minimum pressures, including a member responsive to the pressure to be controlled, a lever operatively connected with said member and with said control element, stop means for halting opposite movements of said lever in positions corresponding to the opposite control functions of said control element, means directly opposing movement of said lever by said member and providing a force in opposition to lever movement by said member increasing with the distance the lever is moved by said member, and means also cooperating with said lever and providing, as the latter is moved in opposition to the force exerted by said member, a resistance to such movement diminishing at a rate more rapid than the rate of reduction in the force exerted by said means for directly opposing movement of said lever during such lever movement, said stop means so arranged that movement of said lever in opposition to the force exerted by said member will be halted when the resistance to such movement by said means also cooperating with said lever is reduced to zero, and means adjustable to vary the rate of change of the resistance presented by said' last mentioned means.

JESS M. BARTHOLOMEW. 

